the cell membrane is able to control what goes in and out of the cell because The plasma membrane surrounding animal cells is where the exchange of substances inside and outside of cells takes place. Some substances need to move from the extracellular fluid outside cells to the inside of the cell, and some substances need to move from the inside of the cell to the extracellular fluid.
Some of the proteins that are stuck in the plasma membrane help to form openings(channels) in the membrane. Through these channels, some substances such as hormones or ions are allowed to pass through. They either are “recognized” by areceptor (a protein molecule) within the cell membrane, or they attach to a carrier molecule, which is allowed through the channels. Because the plasma membrane is choosy about what substances can pass through it, it is said to be selectively permeable.
Permeability describes the ease with which substances can pass through a border, such as a cell membrane. Permeable means that most substances can easily pass through the membrane. Impermeable means that substances cannot pass through the membrane. Selectively permeable orsemipermeable means that only certain substances are able to pass through the membrane.
